this little apache 2 module is for setting an https flag when you are using
reverse proxy

example

 client -> (http/https) -> revproxy -> (http only) -> apache
                                    -> (http only) -> apache

when client connects through https and revproxy adds "HTTPS: something" header,
this module sets an HTTPS flag in apache
makes use of the HTTPS (in php $_SERVER['HTTPS']) variable